Liquid fuel supply unit for a liquid fuel burner and a liquid fuel burner system

ABSTRACT

A liquid fuel burner system and a liquid fuel supply unit ( 101 ) for the liquid fuel burner ( 106 ) of the system are disclosed. The supply unit ( 101 ) comprises a liquid fuel feed pump ( 102 ), a compressor ( 104  and preferably also a motor ( 30 ) mounted on a common drive shaft ( 3 ). The system further comprises a modulatable liquid fuel metering device ( 103 ). The liquid fuel feed pump ( 102 ) is connectable to a liquid fuel conduit from a liquid fuel source, such as an oil tank. An outlet of the feed pump ( 102 ) is connected to an inlet of the liquid fuel metering device ( 103 ), which in turn is connectable to an atomizing nozzle ( 105 ) of the liquid fuel burner ( 106 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of and incorporates byreference essential subject matter disclosed in international PatentApplication No. PCT/DK2003/000733 filed on Oct. 30, 2003 and DanishPatent Application No. PA 2002 01684 filed on Nov. 1, 2002.

FIELD OF THE INVENTION

The present invention relates to a liquid fuel supply unit for a liquidfuel burner and a liquid fuel burner system. Especially the inventionrelates to domestic heating the liquid fuel burner having a heat outputof less than 10 kW.

BACKGROUND OF THE INVENTION

Liquid fuel burners, such as oil burners, are quite common for domesticuse. Ordinarily such oil burners are of the oil pressure atomizing typehaving high-pressure pumps delivering oil at high pressure. Theseburners operate on the principle that when oil under pressure ispermitted to expand through a small orifice, it tends to break into aspray of very fine droplets, which are suitable for combustion. Theseburners are usually designed to operate with oil pressure as high as 3MPa and viscosities of from 2 cSt. The principle upon which theseburners operate requires that the pressure drop across the orifice bemaintained high and as nearly constant as possible in order to achievethe necessary fine atomized droplets and also to avoid pulsatingcombustion. Because it is not possible to maintain the requiredatomization at lower pressure drop and thus lower flow, modulation orregulation of the heat output, in the operation of such burners hastraditionally been very severely limited or has not been used at all,and the burners have been operated in an on-off mode only. This resultsin inferior temperature control, lower boiler efficiency and increasedthermal load of the components, as they will experience a lot of heatingand cooling cycles. On-off regulation also has a detrimental impact onthe environments due to the many start-ups during which the combustionof the fuel is not optimal.

The minimum output of the burner is controlled by the size of the holesin the orifice. The smallest feasible holes are 0.1 mm in diameter, assmaller holes will clog very quickly due to inevitable particles in theoil or due to soot build-up from the combustion, increasing the need formaintenance to an intolerable level. The ordinary minimum output of oilburners having an orifice with the smallest holes possible, is about 10kW, which exceeds the static demand of an ordinary household.

One such oil burner is known from U.S. Pat. No. 5,692,680, whichdiscloses a fuel supply unit for an oil burner. This fuel supply unitcomprises a pump delivering pressurized fuel to a metering orifice,where the flow rate of fuel delivered can be regulated by regulating thepressure differential to maintain a constant flow independently of theelevation of the burner and the elevation of the tank with respect tothe pumping unit. However, it is generally advantageous to have anadjustable flow rate of fuel to the burner, therefore this kind ofsupply unit is not desirable.

It has also been proposed to use burners in which a liquid fuel isgasified prior to the supply to the burner. These burners, however,require a significant start-up time, as the fuel must be heated togasification temperature prior to start-up of the burner, and this kindof burners are mainly used for large industrial burners.

It has also been tried to operate liquid fuel burners on foamed liquidfuel. One such burner is disclosed in U.S. Pat. No. 5,051,090 whereinthe liquid fuel is foamed in a foam collection cylinder. This kind ofburner is, however, only suited for large industrial burners.

EP-A-0 556 694 discloses a burner system for liquid fuel and providedfor easy modulation to compensate for changes in fuel viscosity. Theburner system thus comprises a gas atomizing nozzle fed by an aircompressor and a fuel pump, the fuel being fed through a regulatorregulating on basis of a pressure difference.

U.S. Pat. No. 4,391,580 discloses a system for supplying fuel to apressure atomization fuel oil burner nozzle comprising a rotating gearpump with a rotatable valving structure for delivering fuel at pressurepulses and at a rate depending on the rotational speed of the pump, therate thus being controllable. The system further comprises a blowerdriven by the same motor as the pump.

EP-A-0 013 488 discloses a unit comprising a fuel oil pump, a fan and amotor mounted on a common shaft and an electric circuit for controllingthe unit.

As oil and most other liquid fuels are fossil fuels and hence a scarceresource, care should be taken to exploit the fuel to the utmost.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a liquid fuel burnersystem which when applied to a boiler of a domestic heating systemallows substantially continuous, modulate operation at least during theheating season.

A further object is to provide a unit for use in such a system.

According to the invention a liquid fuel supply unit for a liquid fuelburner with a gas atomizing nozzle, the supply unit comprising a liquidfuel feed pump and a compressor, said liquid fuel feed pump having aninlet connectable to a liquid fuel conduit from a liquid fuel source,such as an oil tank, and an outlet connectable to an inlet of a liquidfuel metering device, said compressor having an outlet being connectableto the gas atomizing nozzle of the liquid fuel burner, is characterizedin that the unit comprise a common drive shaft for the liquid fuel feedpump and the compressor. Hereby is obtained a unit which provides forlow production costs and thus makes it feasible to provide a systemaccording to the invention.

Preferably the liquid fuel feed pump and the compressor both comprise arotary impeller mounted on the common drive shaft.

Also preferably the unit comprises a motor with a rotor connected to thecommon drive shaft. Preferably the motor is placed between thecompressor and the liquid fuel feed pump. This provides for moremaintenance friendly unit as the compressor and liquid fuel feed pumpwill be readily accessible.

The common drive shaft may be one element or it may comprise moreinterconnected shaft elements, which will facilitate manufacturing.

Further the unit may comprise a modulatable liquid fuel metering device,which may comprise a metering orifice and a valve. Alternatively theliquid fuel metering device is a metering pump, which may be a pistonpump activated by an electro magnet.

In a preferred embodiment the compressor is a vane pump and the liquidfuel feed pump may be a gerotor pump.

A liquid fuel burner system according to the invention comprises aburner device with a gas atomizing burner nozzle, a fan for supplyingcombustion air to the burner device, and a liquid fuel supply unit, saidunit being a constructional and exchangeable unit and comprising aliquid fuel feed pump and a compressor having a common drive shaft, thesystem further comprising a modulatable liquid fuel metering device fedby said liquid fuel feed pump, said gas atomizing burner nozzle beingconnected with the liquid fuel metering device and the compressor forreceiving liquid fuel and atomising gas.

By means of the system according to the invention it is economicallyfeasible to run a domestic heating device with a boiler and a liquidfuel burner continuously during the heating season, thus avoiding thedrawbacks related to operation in on-off mode.

Thus the burner device preferably has a minimum heat output of less than10 kW.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be explained in more detail bymeans of embodiments and with reference to the accompanying drawing, inwhich

FIG. 1 is an oblique view of a compressor,

FIG. 2 is an oblique view of a feed pump,

FIG. 3 is a side view of an assembled compressor-pump unit,

FIG. 4 is a cross-section along line IV-IV of the compressor-pump unitin FIG. 3,

FIG. 5 is a partial section along the line V-V in FIG. 4,

FIG. 6 is a diagram showing fuel and air flows in a heating systemutilizing the compressor-pump unit,

FIG. 7 is a diagram showing a preferred embodiment of a liquid fuelsupply unit, and

FIG. 8 shows a section corresponding to FIG. 5 but of a unit in apreferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of illustration, the present invention is embodied in aburner or heating system and a liquid fuel supply unit, such as may beused in pumping a low volume of fuel oil from a tank (not shown) to aburner nozzle in a household boiler.

Thus FIG. 6 shows diagrammatically a heating system with a liquid fuelsupply unit 101 comprising a liquid fuel feed pump 102 connected to ametering device 103 and a compressor 104. The liquid fuel supply unit101 is described in more detail with reference to FIGS. 1-5. Further theheating system comprises a gas atomizing nozzle 105 fed by the supplyunit 101, said nozzle 105 being attached to a burner 106, which issupplied with combustion air by a fan 107. The burner 106 is in turnattached to a boiler 108 of the domestic or household heating system.The boiler 108 and the fan 107 may be of any suitable art. The burner106 and nozzle 105 may also be of a known art.

The fuel supply unit 101, the fan 107, the nozzle 105 and the burner 106together constitute a burner system.

The compressor 104 can be seen in FIG. 1 in partly disassembled state.The compressor 104 is a vane pump having an impeller 2 mounted on adrive shaft 3. The impeller 2 rotates in a housing 4 having an offsetpump chamber 5. On rotation of the impeller 2 movable vanes 6 of theimpeller 2 follows the inner wall of the pump chamber 5, so that gas, inthe present example air, is drawn in through an inlet (not shown),compressed in the pump chamber 5 between the impeller 2, the housing 4and the vanes 6, and delivered through an outlet (not shown). Tofunction the compressor 104 must obviously be equipped with some kind ofcover covering the pump chamber.

In FIG. 2 the feed pump 102 can be seen in partly disassembled state, asno cover is shown. The feed pump 102 is a gerotor pump (a kind of gearwheel pump known in the art) comprising a rotary impeller or gear wheel8 mounted on the shaft 3 to be rotated thereby. The gear wheel 8 mesheswith an internal toothing in an eccentrically mounted gear ring 9,thereby defining pump chambers of varying size to pump a liquid, in thiscase fuel oil, from an inlet to an outlet. FIG. 2 also shows themetering device 103, which in this embodiment is a metering pump,connected to the feed pump 102. The bearing housing 11 of the feed pump102 comprises conduits for delivering oil from the feed pump 102 to themetering device 103 and conduits for the oil delivered from the meteringdevice 103 to a metered oil outlet 12 (FIG. 4) in the bearing housing11. As may be appreciated from FIG. 5 or when comparing FIGS. 1 and 2,the feed pump 102 is mounted on the same drive shaft 3 as the compressor104, so that the housing of the feed pump 102 also act as cover for thecompressor 104. The bearing housing 11 of the feed pump 102 furthercomprises conduits for compressed air from the compressor 104 to anatomizing gas outlet 13 in the bearing housing 11. Between the housing 4of the compressor 104 and the bearing housing 11 of the feed pump 7,gaskets 14 are provided. The gaskets 14 are preferably made of carbonfibre sheet material to provide low friction bearings for the impeller 2and sealing of the housing 4 to hinder leakage of compressed air.

The final assembly is the fuel supply unit 101 comprising the compressor104, the feed pump 102 and a covering 15 of the feed pump 102 can beseen in FIG. 3, which is a side view of the assembly, and also themetering device 103. The extending end of the shaft 3 (FIGS. 1 and 2)can be connected to a preferably electric motor. The motor may be anexternal component, but preferably it is incorporated in the liquid fuelsupply unit 101 as shown at 30 in FIG. 4 and 5. Thus the compressor 104,the feed pump 102 and the motor 30 each have a rotor connected to thecommon shaft 3.

In the section of FIG. 4, it can be seen that the metering device 103 isinserted deeply into the bearing housing 11 of the feed pump 102. Themetering device 103, which in this embodiment is a metering pump,comprises a piston 16 actuated by an electromagnet 17. Oil deliveredfrom the metering device 103 passes a one-way valve, in this case a ball18 biased by a spring 19 to close off the discharge opening of themetering device 103. From the discharge opening of the metering device103, the oil enters a conduit 20 and continues to the outlet 12. Oil forthe feed pump 102 enters through an inlet 21 and flows through conduits(not shown) to the feed pump 102. Excess oil from the feed pump 102 isdirected to an outlet 22 through conduits (not shown) and through apressure regulating valve 23 ensuring that the oil pressure before themetering device 103 is maintained at a desired level e.g. 0.5 baroverpressure (1.5 bar absolute pressure). The output of the meteringdevice 103 can be modulated with a rate of capacity of 1:5 or morebetween minimum and maximum. The modulation may be performed graduallyor stepwise (e.g. two or three stages).

In the section of FIG. 5, it can be seen that the shaft 3 is connectedto the impeller 2 of the compressor and to the gear wheel 8 of the feedpump, which gear wheel 8 meshes with an internal toothing of a gear ring9. The impeller 2 comprises vanes 6 and rotates in the chamber 5 of thehousing 4 of the compressor. In the bearing housing 11 of the feed pump,a conduit 24 for oil delivery to the metering device 103 is formed,whereas excess oil from the pump returns through a conduit 25 to theoutlet 22 (see FIG. 4).

The burner system will comprise means for regulation including means forcontrolling the output from the metering device 103 and means forcontrolling the output of the fan 107 to obtain a proper relationshipbetween the feeding rates of fuel oil and combustion air.

In an example the supply unit, as disclosed with reference to FIGS. 1-5,for a burner of a domestic boiler operates with a feed pump deliveringoil for the metering device at a rate of 20 l/h and at a pressure of 0.5bar (overpressure). Oil for the burner is delivered by the meteringdevice delivering oil at a rate of down to 0.5 l/h at an overpressure of0.5 bar. The metering device is a piston pump, in which the piston isactivated by an electromagnet, and the piston has a displacement of 2.8mm³ per stroke, which at a frequency of 50 Hz gives the above mentionedflow rate. The compressor delivers atomizing air at a rate of 1.3 m³/hat a pressure of 0.3 bar. With this supply unit it is possible to obtainan output of the burner of less than 10 kW at continuous operation ofthe burner.

In stead of a metering pump the preferred embodiment of the liquid fuelsupply unit of the present invention comprises as a metering device anorifice and a valve with a device for opening and closing said valve atintervals according to a heating demand.

Thus FIG. 7 shows a liquid fuel supply unit 101′ comprising a liquidfuel feed pump 102′, a compressor 104′ and a motor 30′ for driving thefeed pump 102′ and the compressor 104′ through a common shaft 3′. Themotor 30′is situated between the compressor 104′ and the liquid fuelfeed pump 102′. The common shaft 3′ may be one element, or it maycomprise two or three elements interconnected by couplings, possiblyelastic couplings as it is known in the art to compensate for minormisalignments. An outlet of the feed pump 102 is through a conduit 201connected to a metering device 103′ comprising a shut-off valve 202 andan orifice 203. A conduit 204 leads fuel metered by the valve 202 andthe orifice 203 to the gas atomizing nozzle 105 and a conduit 205 leadsatomizing air from the compressor 104′ to the nozzle 105. FIG. 7 alsoshows a pressure regulating valve 206 for regulating a pressure dropover the orifice 203 and for draining excess oil delivered from the feedpump 102′.

FIG. 8 shows a section of a unit in the preferred embodiment. Forcorresponding parts the same reference numerals are used as in FIG. 5.It can be seen that the shaft 3′ is connected to the impeller 2 of thecompressor 104′ and to the gear wheel 8 of the feed pump 102′, whichgear wheel 8 meshes with an internal toothing of a gear ring 9. Theimpeller 2 comprises vanes 6 and rotates in the chamber 5 of the housing4 of the compressor. In the bearing housing 11 of the feed pump, aconduit 24 for oil delivery to the metering device 103 is formed,whereas excess oil from the pump returns through a conduit 25 to theoutlet. The electric motor 30′ is situated between the compressor 104′and the liquid fuel feed pump 102′ and comprises a rotor 31 connected tothe shaft 3′ and a stator 32.

In the preferred embodiment shown in FIG. 7 the modulation of the rateof feeding fuel to the nozzle 105 is performed by keeping apredetermined pressure differential across the orifice 203 (and theshut-off valve 202) by means of the pressure regulating valve 206 andopening and closing the shut-off valve 202 to meter or to deliver fuelto the orifice at a pulsing rate in accordance with heat demand. Thismode of operation provides for modulating the heat output from a lowoutput of approximately 1 kW (corresponding to approximately 0.16 l/hfuel oil) to a high output of 10-20 kW or more.

In the alternative the shut-off valve 207 may be kept open and the fueldelivery rate be regulated (metered) by regulating the pressuredifferential across the orifice 208 by means of the pressure regulatingvalve 211.

Whereas the delivery rates of fuel oil from the metering deice 103 andcombustion air from the fan 107 are modulated according to heat effectneeds, the compressor 104 and the feed pump 102 may be run at a constantrate. Thus a constant output from the compressor 104 of 30 l/h at 0.3bar overpressure could be used. This rate corresponds to the need forcombustion air at the low heat output of approximately 1 kW. Thus thecombustion air fan may be turned off when the output from the meteringdevice is modulated to its lower limit.

The described compact design of the supply unit as a constructional unitprovides for easy assemblage during production of burners and also makesthe supply unit ideal for retrofitting on an existing boiler fordomestic use, possibly at a change from using gaseous fuel, such asnatural gas, to a liquid fuel, such as fuel oil. Further the gatheringof components: liquid fuel feed pump, compressor and possibly a liquidfuel metering device in a unit provides for easy exchange of such unitif necessary.

In case a metering pump is used several alternatives to theabove-mentioned metering pump are envisaged:

A piston pump, possibly with commutation, could be used either driven bya separate motor or by the motor driving the compressor and the feedpump. If driven by a separate motor the metering may be modulated byvarying the speed of the motor. Otherwise modulation may be obtained byvarying the commutation.

Also a gear wheel pump with either internal or external gearing teeth,possibly with commutation, could be used either driven by a separatemotor or by the motor driving the compressor and the feed pump. Ifdriven by a separate motor the metering may be modulated by varying thespeed of the motor. Otherwise modulation may be obtained by varying thecommutation.

The invention is not restricted to the use of oil as the liquid fuel,and would work well with other kinds of liquid fuel. Further, theinvention is not restricted to the use of air as the atomizing gas,other kinds of gases, e.g. an inert gas, such as nitrogen, or a gaseousfuel, such as propane, could be used if this should be advantageous inthe given situation.

While the present invention has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisinvention may be made without departing from the spirit and scope of thepresent invention.

1. A liquid fuel supply unit for a liquid fuel burner with a gasatomizing nozzle, the supply unit comprising a liquid fuel feed pump,and a compressor and a motor, said liquid fuel feed pump having an inletconnectable to a liquid fuel conduit from a liquid fuel source, such asan oil tank, and an outlet connectable to an inlet of a liquid fuelmetering device, said compressor having an outlet being connectable tothe gas atomizing nozzle of the liquid fuel burner, wherein the unitcomprises a unitary common drive shaft, the liquid fuel feed pump andthe compressor both comprise a rotary impeller and the motor comprises arotor where the rotary impellers and the rotor are mounted on theunitary common drive shaft for the liquid fuel feed pump and thecompressor.
 2. The supply unit according to claim 1, wherein the liquidfuel feed pump and the compressor both comprise a rotary impellermounted on the common drive shaft.
 3. The supply unit according to claim1, comprising a motor with a rotor connected to the common drive shaft.4. The supply unit according to claim 3, wherein the motor is placedbetween the compressor and the liquid fuel feed pump.
 5. The supply unitaccording to claim 1, wherein the common drive shaft comprisesinterconnected shaft elements.
 6. The supply unit according to claim 1,comprising a modulatable liquid fuel metering device.
 7. The supply unitaccording to claim 6, wherein the liquid fuel metering device comprisecomprises a metering orifice and a valve.
 8. The supply unit accordingto claim 6, wherein the liquid fuel metering device is a metering pump.9. The supply unit according to claim 8, wherein the metering pump is apiston pump activated by an electro magnet.
 10. The supply unitaccording to claim 1, wherein the compressor is a vane pump.
 11. Thesupply unit according to claim 1, wherein the liquid fuel feed pump is agerotor pump.
 12. A liquid fuel burner system comprising a burner devicewith a gas atomizing burner nozzle, a fan for supplying combustion airto the burner device, and a liquid fuel supply unit said unit being aconstructional and exchangeable unit and comprising a liquid fuel feedpump and a compressor having a common drive shaft, the system furthercomprising a modulatable liquid fuel metering device fed by said liquidfuel feed pump, said gas atomizing burner nozzle being connected withthe liquid fuel metering device and the compressor for receiving liquidfuel and atomising gas.
 13. The liquid fuel burner system according toclaim 12, wherein the burner device has a minimum heat output of lessthan 10 kW.